Cryptosporidium parvum (Apicomplexa) has emerged as an important opportunistic pathogen of patients suffering from the Acquired Immunodeficiency Syndrome (AIDS). Gastrointestinal involvement may become so severe in victims of AIDS that death due to diarrheal dehydration and electrolyte imbalance may occur. Our laboratory is currently examining the basic biology of surface and endogenous proteins and glycoproteins of sporozoites of C. parvum, and propose to examine these molecules in more detail. Tbese goals will be accomplished by 1) using currently available monoclonal antibodies (Mabs) as probes to isolate and identify sporozoite proteins and glycoproteins for partial sequence analysis, 2) developing additional Mabs against sporozoite proteins and glycoproteins so that additional parasite molecules can be studied and sequenced, 3) examining whether carbohydrate moieties are a component of epitopes recognized by each Mab, and 4) examining the location of these Molecules on or within sporozoites using immunoelectron microscopy, and 5) construction of both cDNA and genomic libraries to C. parvum for use in sequencing, expressing, and studying functional domains of proteins.